Respiratory #8- Flashcards
In what situations are persons exposed to hypoxic conditions?
- High altitude
- Breath-holding (free diving)
- Disease causing arterial hypoxemia (ex: sleep apnea)
- Poisoning (cyanide, CO) → poison you mitochondria
- Profound anemia
- Shock (circulatory collapse)
What is the difference between hypoxia and hypoxemia?
Hypoxia = shortage of O2 delivery to the tissues
Hypoxemia = arterial blood O2 level are abnormally low, tissues are not necessarily affected
Which cells are responsible for initiating neural activity in carotid bodies?
Type I cells = gloma cells → sense changes in environment → release neurotrasmitters → IX afferent cranial nerve (Glossopharyngeal nerve) → brings the stimulation to the brain stem (pons, respiratory center, medulla)
What are the different cellsand receptors in the carotid body?
Type 1 cells → gloma cells
Type 2 cells → release mediators onto gloma cells (via synapses) → influence activity of gloma cells → activating sensory neurons
Progenitor cells → give rise to the new gloma cells
P2YR → G-protein coupled receptors
P2XR → Ion channel
*Exposure to chronic hypoxia → increase in gloma cells → growth of carotid bodies (Hyperplasia)
What substances are responsible for modulating gloma cell function?
ATP + adenosine → excitatory (released by Type II cells)
Dopamine → inhibitory
Opioids → inhibitory
What mechanisms allow oxygen sensing in the gloma cells?
Oxygen sensing = result of events in the mitochondria:
1. Reduction in PO2 in the region of the mitochondria → less ATP produced → production of lactate (glycolysis to replace oxidative phosphorylation) and ROS within the mitochondria → inhibition of K+ channels
- Decrease in PO2 activates HO-2 (hemeoxygenase-2 enzyme) → production of CO → inhibition of K+ channel
Inhibition K+ channel → depolarization → Ca++ influx → neurotransmitter release
*If depletion of Ca2+ → not hypoxic response
What are different stimulus the glumus cells respond to?
- Hypercapnia
- Acidemia
- Hypoxia
- Lactate
- Hypoglycemia
Other stimulus → Leptin, insulin, temperature, osmolarity, reduced blood flow
*At lower pH, electrical activity is increased
*Gloma cells spike in these environment
How can we artificially stimulate Gloma cells?
- Expose them to hypoxic environment (spikes only if there is calcium, if deplete → stop the response)
- Expose them to NADPH (more H+ ions)
- Expose them to ∆ROS
*Normally there is a balance in NAD, NADP and NADH, NADPH
What are the effects of stimulation of chemoreceptors?
- Increase in phrenic nerve activity and ventilation
- Sympatho-excitation
- Tachycardia or Bradycardia
- Endocrine
- Cardiac (more flow/venous return/vasodialation/contractility)
- Gastrointestinal (
- Metabolic (decrease sympathetic activity)
- Increase hematocrit
What stimulation is necessary for tachycardia to occur?
Occurs when stimulation of carotid bodies + hyperventilation
If hyperventilation, can’t occur (ex: during sleep apnea → airways are blocked) → sympathetic activation → increase in blood pressure
parasympathetic → bradycardiac response to chemoreceptor stimulation
What is the effect of hypoxia on blood vessels?
V/Q is adjusted to ventilation:
Adjusted of perfusion to areas where there is less ventilation
Some pulmonary arteries constrict to ensure the blood is not distributed uselessly to not ventilated area → more constriction → more resistance of pulmonary circulation → Pulmonary hypertension (high BP within pulmonary circulation)
*Effect of hypoxia on blood vessels
What are different gene product associated with pulmonary arterial hypertension?
*Via smooth muscle cells within pulmonary arteries
Endothelin → contraction
TRPC1, TRPC6 Transient receptor potential Ca2+ channel → allow calcium influx → favour contraction (whole family of these that can sense changes in osmolarity, etc.)
What is the effect of continuous vs intermittent hypoxia on HIF?
Continous: Upregulation of HIF-1a and HIF-2a in pulmonary arterial smooth muscle cells → pulmonary hypertension + hypertrophy (increase in size of muscle cells) + hyperplasia (increase in number of muscle cells)
Intermittent: upregulate HIF-1a and down regulated HIF-2a in the carotid body → systemic hypertension
What is the role of mitochondria in the pulmonary artery?
Sensors for Oxygen
Normoxia → favour production of NAD over NADH, H+ ions move into inter-membrane space → diffuse back through ATP-synthase channel
also have O2- → H2O2 → degraded by catalase
Hypoxia → more NADH present, defficiency of H+ ions gradient → decline in membrane potential → les production of ATP, more O2- produced under hypoxia
Explain the oxidized and reduced redox balances and their effect on ion channels?
Oxidative redox balance → balance of NAD+/NADH (favour NAD+), more H2O2, funcitonal K+ channels → keep membrane gradient, Ca2+ no flowing
Reduced redox balance = fall in ATP → decrease NAD+/NADH balance (favour NADH), reduced HO2, K+ channels are blocked → Ca2+ influx (into cytosol) → contraction of smooth muscles
What experiment allowed analysis of hypoxia detection by looking at TRPA1 channels?
EXPERIMENT 1:
1. Mice put in chamber (exposed to hypoxi (15% or 10%) a or room air (21%)) → choice of which chamber to be in
2. Measure time spent in hypoxic chamber → TRPA1 KO mice spent more time than KO in hypoxic chamber
If exposed to 10% → stimulus is strong enough that none of the mice stayed in hypoxic chamber
EXPERIMENT 2:
- Expose to ramp of hypoxia
- Mice have EEG → tell if asleep or awake
Looked to see when they woke up → WT mice had much reduced time for arousal, KO mice did not (wtill very slow to wake up and woke up at lower %O2)
*TRPA1 present in dorsal route ganglia → Xth cranial nerve, no evidence in carotid body → completely different mechanism of detecting hypoxia
How is hypoxia related to Erythropoietin?
Hypoxia → synthesis of erythropoietin
EPO produced in kidney (a bit in the liver)
Hypoxia → inhibition of HIF-PHD → HIF-2a is not degraded → translocated to nucleus → trigger production of EPO → increased hematocrit
*More fetal Hb is synthesized with higher O2 affinity
EPO stimulates bone marrow → produce RBC
How does HIF degradation occur? Why is it important?
It limits production of EPO
Normally HIF-2a associated with VHL (Vin Hippel-Lindau protein) → Proline hydroxylase maintain the links between HIF and VHL → HIF-2a degraded in the proteasome (Rapid HIF turnover)
PHD uses O2 to dissociate the complex → inhibits HIF-2a degradation → transcription of several factors